An absorbent product includes an absorber as its primary component. At present, in most of absorbent products available in the market, the absorber is structured as a single layer of a mixture made of super-absorbent polymer (also referred to as “SAP” hereinafter) and pulp. This single layer structure is sometimes formed with its components uniformly distributed in a single layer, but in general, it just has the appearance of being a single layer.
In other words, these absorbers, whose main component is pulp, are structured, in general, to have a gradient in a concentration distribution of the SAP and the pulp. Specifically, the single layer structure is formed of, most commonly, an upper layer primarily consisting of pulp, a middle layer primarily of SAP, and a bottom layer primarily of pulp, by compressing and bonding these three layers of different constitution from one another into one, and further by the so-called “core wrapping” process in which the above is wrapped with tissue and non-woven fabric, to prevent desorption and scattering of pulp and SAP.
Incidentally, in recent years, research and development in super-absorbent sheet containing fibrous and powder SAP in high proportion as a single-layer-structure absorber has been actively carried out.
For applications that do not require a great absorbing capacity, such as sanitary napkins, slight-incontinence products for women, etc., this super-absorbent sheet is most commonly used as a single layer rather than stacking the sheets to form multiple layers, but for applications that require a great absorbing capacity, such as baby diapers, adult incontinence diapers, etc., the super-absorbent sheets are generally laminated to make a double-layer or triple-layer to give the required absorbing capacity. Because this super-absorbent sheet is much thinner than the afore-mentioned conventional absorber whose main component is pulp, the super-absorbent sheet can be used in a laminate of multiple layers as described above. Moreover, it has an advantage of being far thinner, even when it is used as a laminated structure of multiple layers, than the conventional absorber whose main component is pulp.
In cases where the super-absorbent sheets are laminated to form multiple layers as mentioned above, if the afore-mentioned super-absorbent sheets are simply stacked to form the multiple-layer-structure, due to spaces between respective layers, aqueous liquid such as excreted urine that seeps into the first, or top, layer cannot be uniformly transferred to the second or further lower layers. As a result, it will be difficult to fully function as an absorber. These super-absorbent sheets, therefore, are used, in case these super-absorbent sheets are laminated to form multiple layers, by making them into one body using adhesive or other bonding material. Thus the extremely thin absorber with a great absorbing capacity potential can be obtained by laminating the super-absorbent sheets in multiple layers.
In real-life situations, however, the absorber which can be obtained by laminating the super-absorbent sheets in multiple layers has a disadvantage that its absorbing speed cannot keep up with the speed of the excreted liquid that flows into the absorber, which results in its leaking easily, without exerting its inherent absorbing capability.
According to the research by the inventors of the present invention, a limit of the speed of absorption by swelling of the SAP due to characteristics of the SAP and the aqueous liquid, and insufficient space for liquid retention due to the absorber's extreme thinness are cited as causes for the disadvantage described above. In addition to these, it has also been identified that the overall rate of utilization of the absorbent is lowered by SAP's tendency to cause blocking, on top of its slow absorbing speed, though its absorbing capacity is extremely high in comparison to the pulp, the main component of the conventional absorber, whose absorbing capacity is small though its absorbing speed is high.
Because in case two or more super-absorbent sheets are laminated, the above problem becomes even more evident, research for a method of making the aqueous liquid fed to the top super-absorbent sheet seep into other super-absorbent sheets quickly and uniformly have been conducted and a technique of inserting between respective layers highly hydrophilic non-woven fabrics as diffusion sheets, a technique of physically making large apertures or cutting slits and the like have been proposed, but so far no effective solution has been found. With this background, while an advent of absorbent products comprising the laminated super-absorbent sheets in multiple layers has been desired, it has not yet been realized so far.